This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-342102 filed on Nov. 7, 2001.
The present invention relates to an electrical load disconnection detecting apparatus.
An electrical load disconnection detecting apparatus is shown in FIG. 8. This apparatus is especially used in a vehicle for detecting disconnection of electrical loads, such as taillights or stoplights. The apparatus includes a differential amplifier circuit 14, a noninverting amplifier circuit 16, and a microcomputer 18. A resistor 12 for current-voltage conversion is connected in series with a path for supplying a current to lamps L1-Ln.
Voltages that appear at each end of the resistor 12 are inputted to the differential amplifier circuit 14. An output Vout1 of the differential amplifier circuit 14 is amplified by the noninverting amplifier circuit 16. The amplified voltage Vout2 is inputted to the microcomputer 18 and compared with a reference to determine whether disconnection exists.
In this apparatus, two amplifiers 20, 25, one is for the differential amplifier circuit 14 and the other is for the noninverting amplifier circuit 16, are required. This makes the apparatus large and costly.
The present invention therefore has an objective to reduce the size and the cost of the electrical load disconnection detecting apparatus.
The electrical load disconnection detecting apparatus of the present invention includes a resistor for current-voltage conversion, a differential amplifier circuit, a disconnection detecting device, and a charge pump circuit. The resistor is connected in series with a path for supplying power to an electrical load to be monitored. Voltages that appear at the ends of the resistor are inputted to the differential amplifier circuit. The charge pump circuit increases the battery voltage and supplies the increased voltage to an operational amplifier included in the differential amplifier circuit.
Because the operational amplifier is supplied with the amplified operating voltage, it can output an amplified output voltage to the detecting device. Therefore, the detecting device can perform accurate detection. Furthermore, the charge pump circuit can be constructed small and at low cost as compared with the noninverting amplifier circuit.